1. Field of the Invention
The present invention relates to a toner technology used for electricphotography, electrostatic records and electrostatic printing, more particularly to a method for manufacturing toner that has a stable particle size and a sharp particle size distribution, a toner manufactured using the method, an image forming method and image forming apparatus using the toner.
2. Description of the Related Art
A developer used for electrophotography, electrostatic recording and electrostatic printing is once attached to, for example, an image bearing member such as a photoconductor having a latent electrostatic image formed thereon in a developing step, then the image is transferred from the photoconductor to a transfer medium such as transfer paper in a transfer step, thereafter the image is fixed onto a paper surface in a fixing step.
Developers used for developing latent electrostatic images formed on latent electrostatic image-bearing surfaces of photoconductors are of two types: a two-component developer composed of carrier and toner, and a one-component developer composed of magnetic or non-magnetic toner requiring no carriers. These developers are known as dry toners. As the dry toner used for these electric photography, electrostatic recording and electrostatic printing purposes, those toners have been used that are prepared by melt-kneading toner binder, such as styrene based resin or polyester based resin, together with colorant and by finely pulverizing the resulting kneaded product.
Generally, a method for reducing the particle diameter of toner is employed for improving image quality in order to obtain high-definition and high quality images.
However, phenomena have occurred in such that the toner is further pulverized and thereby extremely fine particles are generated and/or image quality becomes deteriorated since fluidizer is embedded on the toner surface because of 1) an irregular particle shape of the toner to be obtained in case of using a manufacturing method according to a normal kneading and pulverizing method, 2) stress stirred with the carriers in the developing unit of an image forming apparatus in case of using the dry toner as a two-component developer, or 3) stress in contact with a developing roller, a toner supply roller, a layer thickness regulating blade, and a frictional electrification blade in case of using the same as a one-component developer.
A toner with an irregular particle shape is an obstruction factor for downsizing the apparatus since its fluidity is so poor as a powder that necessity of increasing fluidization is generated, or the fill up rate of a toner bottle with toner is low. Therefore, an advantage of a reduced particle diameter cannot be effectively provided now. A problem arises in manufacturing toner particles by means of a pulverizing method: There is a limitation as to an obtainable particle diameter and thus further downsizing of particle diameter cannot be effected.
In order to cover defects caused by such irregular particle shapes, various methods for manufacturing spherical toner are proposed. For example, methods generally used include a polymer suspension method and an emulsion method. Such manufacturing methods include a step of emulsifying an oil phase, which has been prepared by dissolving or dispersing colorant (e.g., resin and pigment) and toner components (e.g., wax) into an organic solvent (including monomer), by mixing it with an aqueous phase by means of a mechanical emulsifying means to form toner particle-sized liquid droplets.
In case of using a toner manufactured by a suspension method or an emulsion method, the emulsified liquid generates liquid droplets while repeating the equilibrium reaction between atomization by shearing and integration of atomized particles, and the size of the particle diameter and the particle size distribution is temporarily determined when balance of the atomization and coalescence are kept.
As a major factor by which the size of the toner particle diameter and the particle size distribution are determined in this case, considered are energy at the time of shearing; the energy is given to the raw materials supplied by an emulsion machine, and total shearing energy per feed unit flow rate of raw materials; the total shearing energy is given during equilibrium reaction between atomization of particles by shearing and integration of the atomized particles.
However, problems have arisen that differences occur between particle diameter (volume average particle diameter) and particle size distribution during the emulsifying step because different toner formulations offer different equilibrium rates between atomization by shearing and integration of the atomized particles, and as such optimal conditions cannot be obtained. Although a method is used in order to deal with these problems for adjusting the volume average particle diameter of toner and the particle size distribution and aligning them to the target values as a post-step, including the step of cutting dust-sized particles and rough-sized particles, problems have arisen including complicated manufacturing steps with longer amount of time required and the worsening of efficiency.
As a method for improving the size of toner particles and the particle size distribution, the following methods are discussed.
For example, a method is discussed for manufacturing a toner with no variation of performance between the sharp particle size distribution and the particles by means of using a stirring layer equipped with stirring blades in the upper, lower and adjacent positions; including the stirring blades in the upper position provided antecedent to a rotating direction at an intersection angle less than ninety degrees to the stirring blades in the lower position. (Refer to Japanese Patent Application Laid-Open (JP-A) 2000-321821 for example.)
A method is also discussed for manufacturing a polymerization toner that provides sharp particle size distributions after the polymerization by means of controlling blade tip speed during polymerization reaction, depth of the stirring blade mounted on the top from the water surface, and stirring power requirement during the polymerization into a specific range (see JP-A No. 2001-125309, for example).
Another method is discussed for effectively manufacturing a toner that has a sharp particle size distribution by means of setting relations between volumes V (m3) of fluid materials present in a granulation vessel and applied motive power P (kW) of the stirring apparatus into 15<P/V<100. (Refer to JP-A No. 2002-91071, for example.)
The above described methods control shapes, arrangement and stirring power of the stirring blades and form the toner particles as the target values; however, it is difficult to mention that these methods granulate with the consideration of coalescence behavior acquired as an important factor of the granulating mechanism according to so-called the present invention as described below. In other words, these methods control the toner particles without considering the equilibrium between atomization of toner particles by shearing power and integration of atomized particles. Therefore, these methods are insufficient for manufacturing a toner that has further stable particle diameter and sharp particle size distribution.